Two-color radiometer

ABSTRACT

The inventive radiometer is capable of measuring the radiant energy of a target or of an event, including a transient event, in two spectral regions with identical fields of view. The invention may be used for target identification or for discriminating against false targets, such as solar radiation.

United States Patent Taczak, Jr.

TWO-COLOR RADIOMETER Inventor: William J. Taczak, Jr.,

Fredericksburg, Va.

Assignee: The United States of America as represented by the Secretary of the Navy Filed: April 7, 1971 Appl. No.: 132,036

u.s.c1.*...' ..250/83.3H

Int. Cl. ..G0lt 1/16 Field of Search ..250/83.3 H; 356/81, 82

[451 Oct. 17,1972

[56] References Cited UNITED STATES PATENTS 3,204,100 8/1965 Wormser et al. .....250/83.3 H 3,39l,279

Primary Examiner-James W. Lawrence Assistant Examiner-Davis L. Willis Attorney-R. S. Sciascia and Thomas 0. Watson, Jr.

[57] ABSTRACT The inventive radiometer is capable of measuring the radiant energy of a target or of an event, including a transient event, in two spectral regions with identical fields of view. The invention may be used for target identification or for discriminating against false targets, such as solar radiation.

8 Claims, 1 Drawing Figure 7/1968 Detrio ..250/83.3 H

P'A'TE'N'TEDncI 11 I372 INVENTOR.

WILL/AM J TAGZA/QJR.

ATTORNEY TWO-COLOR RADIOMETER STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION A. Field of the Invention v The present invention relates generally to devices for detecting and measuring radiant energy and more particularly to devices that are capable of detecting and measuring radiant energy of an event simultaneously in two spectral regions with identical fields of view.

B. Description of the Prior Art Two-color radiometric systems have been used to distinguish a radiating target from false targets, especially in the infrared spectrum, in the priorarLln some systems, two complete units are used, one for each color. These are usually quite cumbersome and complex devices; and in most cases, the fields of view are not identical. A number of these two-color units are encased in the same housing and view the same angular field. A rotating chopper blade alternates the incident radiant energy in regular intervals between the two detectors. Obviously, this type of device cannot be used to measure a transient eventsince the output signals of the two detectors do not correspond in time.

SUMMARY OF THE INVENTION The inventive radiometer is capable of measuring the radiant energy of an event, especially a transient 'event, in two spectral regions with identical fields of view. The inventive radiometer may also be used to identify targets and to discriminate against false targets such as solar radiation. These functions are accomplished in the inventive system by providing a collector lens to collect the incident radiant energy and to focus it to an image of the source. A doublet lens is placed at the focus of the collector lens to transfer the radiation to a highly-reflective conical shield that receives the transferred radiant energy and scrambles and spreads the radiant energy evenly over the surfaces of two detectors. Spectral filters are provided for each detector to transmit radiant energy in the spectral regions of interest. The outputs from the detector are fed to a differential amplifier and from there through a diode. The inventive system discriminates against solar radiation, while detecting true targets.

OBJECTS OF THE INVENTION An object of the present invention is the provision of a simple system to detect and measure the radiant energy of an event.

Another object of the invention is to provide a lowing detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The FIGURE illustrates a preferred embodiment of the inventive two-color radiometer.

DESCRIPTION OF THE PREFERRED EMBODIMENT The FIGURE illustrates a preferred embodiment of the inventive two-color radiometer. The two-color radio-meter 1 comprises a collector lens 2 for collecting the incident radiant energy and for focusing the radiant energy to an image of the source. The field doublet lens 3 is placed at the focus of the collector lens and transfers the incident radiant energy to a highly reflective conical shield 4 that acts asa light and radiant energy scrambler and spreads the radiation over the surface of the two radiant energy detectors 7. The spectral filters 5 and 6 are selected to transmit radiation in the two spectral regions of interest. The

I choice of detectors 7 depends upon the spectral regions of interest and may or may not be of the same material. An electrical signal representative of the incident radiant energy passes from the detectors 7 through preamplifiers 8 to differential amplifier 9. From the differential amplifier 9, the resultant signal passes through diode 10.

A specific embodiment of the instant invention will now be described that can be used to detect radiation from a source which can be characterized as a blackbody radiator radiating from 800 to 1,300 K and which can discriminate against solar radiation. A germanium collector lens 2 acts as a 1.8 micrometerlongpass filter. A germanium field doublet lens 3 is positioned at the focus of the germanium collector lens 2 and transfers the incident radiant energy to the conical shield 4 which scrambles the light and incident radiant energy and spreads this evenly over the surface of the two detectors 7. The twodetectors 7 are lead sulfide detectors and are identical having equal areas accepting radiation. Spectral filter 5 is designed to transmit radiation in the spectral band from 1.8 to 2.1 micrometers. Spectral filter 6 is designed to transmit radiation in the spectral band from 2.2 to 2.5 micrometers. The preamplifiers 8 are identical and have the same gain setting. The resultant signals from the lead sulfide detectors 7 and preamplifiers 8 are fed into a differential amplifier 9 for comparison. If the incident radiant energy is solar radiation, it can be shown from Plancks black-body equations that there will be more radiation in the 1.8 to 2.1 micrometer region than in the 2.2 to 2.5 micrometer region. Thus, the output signal from the differential amplifier will be negative. However, the

diode 10 will block a negative signal; thus, the system will not permit an output signal representative of solar radiation. A black-body radiator between 800 and l300 K has more radiation than the 2.2 to 2.5

micrometer band region then the 1.8 to 2.1 micrometer band region. Thus, the differential amplified output from a signal representative of this type of radiation will be positive; and the diode 10 will permit the signal to pass, denoting a true source.

tive system is that the power density and the spectral content of the incident radiant energy impinging on the spectral filters are thesame because the highly reflective conicaltshield {scrambles .the incident light and radiant energy and spreads it evenly over the spectral filters 5 and 6. Thus, it is seen that a rather. simple, highly'reliable system is provided for identifying true targets and discriminating against false targets, such as a germaniumcollector lens for collecting and trans? mitting incident radiant energy of a wavelength equal to or greater than 1.8 micrometers and for focusing this radiant energy ,to an image of its source; l

a germanium field doublet lenslocated at the focus of the collector lens for transferring the transmitted radiant energy;

two identical lead sulfide detectors capable of emitting an electrical signal responsive to the received radiant energy;

a highly-reflective conical shield capableof scrambling light and other incident radiant energy and of spreading the incident radiant energy over the surface of the two detectors;

two spectral filters for transmitting radiant energy to each of the detectors, one of said filters capable of transmitting radiant energy in the 1.8 to 2.1 micrometer region to one of said detectors and the other of said filters capable of transmitting radiant energy in the 2.2 to 2.5 micrometer region to the other of said detectors;

an amplifier electrically connected to each of said detectors for amplifying the. resultant electrical signal from said detectors;

a differential amplifier for receiving the amplified electrical signals from each of said detectors; and

a diode capable of transmitting an electrical signal when the detected radiant energy lies primarily in the 2.2 to 2.5 micrometer region and capable of blocking the transmission of an electrical signal when the detected radiant energy lies primarily in the 1.8 to 2.1 micrometer region.- I

2. A new and improved radiometer comprising:

means for detecting and measuring the radiant energy of an event in-plural spectral regions with identical fields of view; and

means for discriminating against undesired sources of radiant energy; wherein said detecting and measuring means comprisesz I v 4 means for collecting incident radiant energy and p focusing the incident radiant energy to an image of the source; a means located at the focus of the collecting means for transferring the incident radiant energy; plural means for emitting electrical signals in response to the impingment thereon of radiant y; means for receiving the transferred radiant energy and for scrambling and spreading the transferred radiant energy evenly over the surface of the plural responsive means; and plural means for receiving the radiant energy from the scrambling and spreading means and for transmitting to the responsive means only that radiant energy that lies in plural distinct spectral regions of interest, each of said transmitting means transmitting a different radiant energy 3.A device as recited in claim 2 further comprising amplifying means for amplifying the electrical signals from the responsive means and means for transmitting an electrical signal upon the detection of a desired source of radiant energy and for blocking the transmission of an electrical signal upon the detection of radiant energy from an undesired source.

4. A device as recited in claim 2 in which the collecting means is a germanium collector lens capable of acting as a 1.8 micrometer long-pass filter.v

5. A device as recited in claim 2 in which the means for transmitting radiant energy in plural spectral regions of interest comprises two spectral filters, one.

capable of transmitting radiant energy in the 1.8 to 2.1 micrometer region and the other capable of transmitting radiant energy in the 2.2 to 2.5 micrometer region.

6. A device as recited in claim 2 in which the respone sive means comprises two identical lead sulfide detectors with equal areas for excepting radiant energy.

7. A device as recited in claim 2 in which the means for transmitting and for blocking an electrical signal comprises a differential amplifier and a diode.

8. A device as recited in claim 2 in which the scrambling and spreading means comprises a highly reflective conical shield. 

1. A new and improved two-color radiometer comprising: a germanium collector lens for collecting and transmitting incident radiant energy of a wavelength equal to or greater than 1.8 micrometers and for focusing this radiant energy to an image of its source; a germanium field doublet lens located at the focus of the collector lens for transferring the transmitted radiant energy; two identical lead sulfide detectors capable of emitting an electrical signal responsive to the received radiant energy; a highly-reflective conical shield capable of scrambling light and other incident radiant energy and of spreading the incident radiant energy over the surface of the two detectors; two spectral filters for transmitting radiant energy to each of the detectors, one of said filters capable of transmitting radiant energy in the 1.8 to 2.1 micrometer region to one of said detectors and the other of said filters capable of transmitting radiant energy in the 2.2 to 2.5 micrometer region to the other of said detectors; an amplifier electrically connected to each of said detectors for amplifying the resultant electrical signal from said detectors; a differential amplifier for receiving the amplified electrical signals from each of said detectors; and a diode capable of transmitting an electrical signal when the detected radiant energy lies primarily in the 2.2 to 2.5 micrometer region and capable of blocking the transmission of an electrical signal when the detected radiant energy lies primarily in the 1.8 to 2.1 micrometer region.
 2. A new and improved radiometer comprising: means for detecting and measuring the radiant energy of an event in plural spectral regions with identical fields of view; and means for discriminating against undesired sources of radiant energy; wherein said detecting and measuring means comprises: means for collecting incident radiant energy and focusing the incident radiant energy to an image of the source; means located at the focus of the collecting means for transferring the incident radiant energy; plural means for emitting electrical signals in response to the impingment thereon of radiant energy; means for receiving the transferred radiant energy and for scrambling and spreading the transferred radiant energy evenly over the surface of the plural responsive means; and plural means for receiving the radiant energy from the scrambling and spreading means and for transmitting to the responsive means only that radiant energy that lies in plural distinct spectral regions of interest, each of said transmitting means transmitting a different radiant energy spectral region.
 3. A device as recited in claim 2 further comprising amplifying means for amplifying the electrical signals from the responsive means and means for transmitting an electrical signal upon the detection of a desired source of radiant energy and for blocking the transmission of an electrical signal upon the detection of radiant energy from an undesired source.
 4. A device as recited in claim 2 in which the collecting means is a germanium collector lens capable of acting as a 1.8 micrometer long-pass filter.
 5. A device as recited in claim 2 in which the means for transmitting radiant energy in plural spectral regions of interest comprises two spectral filters, one capable of transmitting radiant energy in the 1.8 to 2.1 micrometer region and the other capable of transmItting radiant energy in the 2.2 to 2.5 micrometer region.
 6. A device as recited in claim 2 in which the responsive means comprises two identical lead sulfide detectors with equal areas for excepting radiant energy.
 7. A device as recited in claim 2 in which the means for transmitting and for blocking an electrical signal comprises a differential amplifier and a diode.
 8. A device as recited in claim 2 in which the scrambling and spreading means comprises a highly reflective conical shield. 